Since I know you are returning to Bangkok soon; Here you have plenty of official places of Apple ( apart from the many knockout ones) Ill give you a couple to start with:

-Take the BTS to Asok station, go downstairs to the MRT and take it to Phraram 9 Station. Take the exit that says “fortune tower” Once outside is your building on your righhand side. Go to the 3rd floor and follow the corridors when you get off the stairs to your left. Continue the corridor and pass the multiple stores of pirate programs,cd’s and movies (if your interested in that each copy costs around 300thb) and you will get to a round like hall full of computer stores. Apple shop is right beneath the escalator.

-Take the BTS to Siam Station, and go to exit 2 to Siam Paragon, in there take the escalators to the 3rd floor, and in your far left you will see iStudio Store ( next to Kinokuniya book store)